1. Technical Field
The present invention generally relates to methods and systems for reducing the risk of collisions between aircraft and terrain. Such systems and methods inform a pilot of a degree of change in flight to avoid colliding with terrain.
2. Background Art
Ground Proximity Warning Systems (GPWS), Ground Collision Avoidance Systems (GCAS), and/or Terrain Awareness and Warning Systems (TAWS), are used in aircraft to inform pilots or other flight crew members of a likely or imminent collision with terrain. For simplicity, these systems are collectively and generically referred to herein as TAWS. TSO-C151a (Technical Standard Order) and RTCA DO-161A, incorporated herein by reference, including Appendices, prescribe minimum operational performance standards for TAWS equipment.
TAWS includes a Forward Looking Terrain Avoidance (FLTA) function which looks ahead of an aircraft along and below the aircraft's lateral and vertical flight path and provides alerts to a flight crew if a potential Controlled Flight Into Terrain (CFIT) threat exists. CFIT is an aircraft accident where a completely airworthy aircraft is flown into terrain (which may include man-made obstacles) or water. In the United States, Class A TAWS equipment is required to provide terrain information on a display, such as a weather radar indicator, or other video output device. In display, such as a weather radar indicator, or other video output device. In such a system, visual and aural signals are provided to a flight crew for both caution and warning alerts in one or more of the following situations:
(1) excessive rate of descent
(2) excessive closure rate to terrain;
(3) negative climb rates/loss of altitude after take-off;
(4) unsafe clearance when not in landing configuration;
(5) excessive downward deviation from an ILS (Instrument Landing System) glideslope;
(6) CFIT threats; and
(7) when an aircraft is hazardously below the normal (typically three degree) approach path for the nearest runway.
A “caution alert” as used herein is provided when a potentially hazardous flight condition with terrain is detected, immediate crew/pilot attention is warranted, and a potential for crew/pilot action exists. In a TAWS, a typical caution alert is in the form of an audible notification of a flight condition, e.g., “terrain ahead” and includes corresponding visual indicators of the flight condition such as an amber or yellow light on a display. A “warning alert” as used herein is provided by a TAWS when a potentially hazardous flight condition with terrain is detected and immediate crew/pilot action is required to avoid the hazardous flight condition.
Typically, a warning alert may be in the form of an audible instruction to take action (e.g., “terrain, terrain; pull up, pull up”) and corresponding visual indicator (e.g., a red light or symbol on a cockpit display) notifying a crew or pilot that action is required to avoid an imminent threat. In most instances a warning alert is only provided after a caution alert is provided. The differences between these alert types are made primarily to distinguish between severities of terrain threats encountered during flight.
Forward Looking Terrain Avoidance (FLTA) uses a “look ahead” or “sensor” profile to determine whether to generate caution and/or warning alerts. The sensor profile is a three dimensional mathematical model of potential future aircraft position and is compared with terrain data to determine whether a potential for collision with terrain exists. If terrain data intersects or conflicts with the sensor profile then a caution alert or warning alert is given to the flight crew. The differences between a caution alert and a warning alert are generally related to the proximity in time or distance of the terrain to the aircraft. For example, a sensor profile for a caution alert may extend further in time or distance from the aircraft position than the sensor profile used for generating a warning alert.
Referring now to FIG. 1, an example of conventional TAWS functionality will be described. The FLTA function of the TAWS in aircraft 10 compares the sensor profile 15 (also referred to herein as “terrain avoidance profile”) with numerical models of terrain features, for example mountain 50, stored in a database. For the sake of simplicity, the FLTA described herein relates to terrain avoidance profiles 15 used in association with generating a warning alert. However, profile 15, as well as other types of profiles discussed herein may be used for generating either a caution alert or a warning alert.
When profile 15 for aircraft 10 at position (A) encounters terrain feature 50 (i.e., the model of flight position intersects the model of terrain), the TAWS in aircraft 10 issues a warning alert including aural alert 25 such as “terrain; pull up, pull up.” The pilot of aircraft 10 reacts to the warning alert by enacting a terrain avoidance maneuver, for example, changing the flight path for increasing elevation of aircraft 10 through positions (B) and (C) until profile 15 no longer encounters with terrain feature 50. At this point (shown at position (D)), aural alert 25 ceases and the pilot may stop increasing the elevation of aircraft 10 to overcome terrain feature 50.
This conventional TAWS suffers from several problems. By way of example, when visual inspection by a pilot is impossible or retarded (e.g., fog, darkness, or other visually impairing condition), a pilot may be entirely surprised by a terrain warning alert. Since conventional terrain alerts do not articulate any details about the collision threat, the pilot may enact a rigorous increase in elevation to avoid the threat of collision with terrain. Moreover, in many conventional TAWS the warning alert is continuously repeated until aircraft 10 reaches an elevation high enough to overcome terrain 50. In this case, the pilot may continue the most rigorous increase in elevation possible until the terrain threat is overcome. Severe flight path alterations, such as attempting or continuing rigorous increases in climb angle, may: (i) induce aircraft 10 to stall (which actually increases the chance of collision with the terrain); (ii) lead to injury of passengers and/or flight crew; (iii) damage cargo and/or the aircraft; (iv) cause unnecessary stress on the pilot and/or flight crew; and/or (v) result in an uncomfortable ride.
With the conventional terrain warning methods and systems, a pilot may unnecessarily enact extreme terrain avoidance maneuvers and may not realize that danger has subsided until the aural alert ceases, even though in reality, a timely response by the pilot and a slight or gradual increase in altitude might avoid the terrain.